I Hate Asking Stupid Questions......But

[blown240]

I hate to ask stupid questions, but I've searched and can't find the answer.

I put power steering in my 61. The new pitman arm doesn't have a hole for the cotter pin, so I want to put a nylock on it, as I found when I searched.

The problem is that I don't know what size it is. I read 7/8-14, but thats HUGE compared to this.

Does anyone know the size of this nut, or should I just put some red or blue loctite and torque down the castle nut?

Thanks!